For BPA, Does the Dose Make the Poison?

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For those who keep up with environmental health research and chemical regulations, it is no surprise to come across conflicting reports on the safety or risk of various compounds. This week, in the case of the compound bisphenol A (BPA), these conflicting reports happened to emerge almost simultaneously. On January 21st, the European Food Safety Authority declared that BPA “poses no health risk to consumers of any age group…at current exposure levels.” The next day, a study published in the journal PLoS Genetics showed that even low and short-term exposures to BPA and other hormone-mimicking compounds could alter stem cells and lead to lower sperm counts.

BPA is a common ingredient in plastics used for food and drink containers. Its hormone-like properties allow it to disrupt the endocrine system, with potential health effects ranging from reproductive issues to cancer. Though BPA has been banned in baby bottles in the U.S., and BPA-free products have become widely available since concerns about the compound were first raised in 2008, it remains in products from water bottles to the inside coatings of cans.

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David McNew via Getty Images

‘The dose makes the poison’ is a well-known adage in toxicology, implying that even hazardous chemicals can be harmless at low enough concentrations. However, decades of research have shown this to be an overly simplistic way of analyzing toxic exposures.  Dr. Theo Colborn, who passed away on December 14th, 2014, was a pioneering researcher in the field of endocrine disruption and a tireless advocate for precautionary chemical regulation. Her research on endocrine disruption demonstrated that even very low concentrations of harmful chemicals could result in changes to the reproductive system, particularly in developing babies and children who have less of a tolerance for exposure than adults. She also demonstrated that not all effects of toxic chemicals are immediately apparent, but can occur decades and even generations later.

The study published last week focused on both questions of concentration and timing. The researchers tested estrogenic compounds including BPA on mice, and found that they alter the stem cells, or undifferentiated cells, which are responsible for sperm production later in life. Patricia Hunt, the researcher who led the study, told Environmental Health News that exposure to even low doses of estrogens “is not simply affecting sperm being produced now, but impacting the stem cell population, and that will affect sperm produced throughout the lifetime.”

Uncertainties remain in the wake of this study. For instance, the researchers are still investigating whether the changes observed can cross generations, or whether the same changes can occur in human reproductive stem cells. The EFSA also recognized uncertainties in non-dietary sources of BPA, and they are still conducting long-term studies in rats. While scientists and regulators continue to chase answers, this past week shines a spotlight on the complicated realm of environmental health risk assessment, and shows the continued relevance of Dr. Theo Colborn’s work and legacy. Dose is indeed important in making a poison, but so is timing of exposure, and time itself in revealing the chronic and transgenerational effects of chemicals.

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